Diagnostic comparison of water tree growth in XLPE insulated power cables produced in GCC countries

Document Type : Original Article

Authors

1 College of Engineering, King Saud University, Riyadh, Saudi Arabia.

2 Riyadh Group of Cables, Riyadh, Saudi Arabia.

3 King Abdualaziz City for Science and Technology, Riyadh, Saudi Arabia.

4 Saudi Electricity Company, Riyadh, Saudi Arabia.

Abstract

Abstract:
Electric power utilities and industrial units in Saudi Arabia are extensively using XLPE
cables produced in the Arabian Gulf region. Due to prevailing high temperatures and
high sulphate content in the soil coupled with high sub surface water table, these cables
have suffered serious breakdowns in a short time span after their installation. This
investigation was undertaken to compare the resistance to water treeing in of kV, XLPE
insulated cables of four regional manufacturers that are producing these cables
according to international standards. In first stage, aging was carried out under high
electric stress and temperature cycling in the presence of deionized water. After 120
days of this aging, their remaining dielectric strength was determined. These results
showed poor performance of one type while the others exhibited close values. In the
second stage, the cables were aged in the presence of aqueous ionic solution of CuSO4
for aging periods that lasted in the range of 500 to 1500 hours. Water tree population
and tree lengths were compared and their number and length distributions were
subjected to statistical Weibull and Log-normal models. Water tree population and their
length distributions were found to fit better on Log-normal model. This suggests that the
most likely mechanism for environmentally induced water tree degradation is electromechanical
fatigue based. On the other hand, water tree density as a function of aging
period was found to obey a log-linear relation. These data also show that water tree
density in these cables as evaluated in the second stage of aging, comparatively varies
significantly and leads to better segregation and selection of the cable that will serve the
best in such environmental conditions.

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